Antennas for implantable medical devices

ABSTRACT

In general, techniques are described for wirelessly transferring information using an implantable antenna. In one example, an apparatus includes an implantable medical device that includes a housing including an implantable telemetry circuit. The apparatus includes a dielectric compartment, mechanically coupled to the housing and including first and second substantially parallel face portions, and a third face portion extending between the first and second face portions, and an antenna assembly configured to be mechanically attached to the dielectric compartment and configured to be electrically coupled to the implantable telemetry circuit, the antenna assembly includes a spiral conductor comprising first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment, where the first, second, and third spiral conductor portions define an interior region, and where at least a portion of the third spiral conductor portion extends inwardly into the interior region.

CLAIM OF PRIORITY

This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 61/832,264, filed on Jun. 7, 2013, which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure relates generally to medical devices and, in particular, to antennas for implantable medical devices.

BACKGROUND

Implantable medical devices (IMDs) can perform a variety of diagnostic or therapeutic functions. In an example, an IMD can include one or more cardiac function management features, such as to monitor the heart or to provide electrical stimulation to a heart or to the nervous system. The cardiac function management features can be used to diagnose or treat a subject, for example, in cases of electrical or mechanical abnormalities of the heart. Examples of IMDs can include pacers, automatic implantable cardioverter-defibrillators (ICDs), cardiac resynchronization therapy (CRT) devices, implantable monitors, neuromodulation devices (e.g., deep brain stimulators, or other neural stimulators), cochlear implants, or drug pumps, among other examples.

Such IMDs can include electronic circuitry configured to wirelessly transfer information between implanted IMDs, or between an IMD and an assembly external to the body. Such information can include, for example, programming instructions or configuration information to configure the IMD to monitor, diagnose, or treat a physiologic condition. Such information can also include data sensed, detected, or processed by the IMD and transmitted to another device or assembly (e.g., physiologic information, a disease status, etc.) An IMD can include an antenna sized and shaped to wirelessly transfer information using a desired operating frequency range. Such a frequency range can be specified by a spectrum allocation authority within the country where the IMD may be located or used. Thus, the IMD generally includes an antenna tailored to the spectrum allocation regulations where the IMD may be used or sold.

OVERVIEW

Generally, active implantable medical devices (IMDs) can include a pacemaker, a defibrillator, a cardiac resynchronization therapy device, a neurostimulation device, an implantable monitoring device, or one or more other devices. Information can be wirelessly transmitted to, or received from, such IMDs, such as using electromagnetic waves. Such electromagnetic waves can be transmitted or received using an implantable antenna included as a portion of the IMD. Such electromagnetic transmission can provide an effective communication range on the order of meters, as compared to using a communication scheme involving mutual-inductive magnetic coupling. Such magnetic coupling is generally limited to an effective communication range of only centimeters.

In Zart et al. (U.S. Pat. No. 7,309,262), a connector assembly for an implantable medical device is mentioned. The connector assembly includes a core element formed of a thermoplastic material, and a circuit member including an antenna structure extending over a portion of the core element outer surface.

In Abadia et al., “3D-Spiral Small Antenna Design and Realization for Biomedical Telemetry in the MICS band,” Radioengineering, vol. 18., no. 4, (December 2009), pp. 359-367, a dielectric-loaded antenna including a coaxial feed, a ground plane, and a grounding pin between a metal patch portion of the antenna and the ground plane are provided.

In Kwak, “Ultra-wide band Spiral shaped small Antenna for the Biomedical Telemetry,” APMC2005 Proceedings, Institute for Electrical and Electronics Engineers (2005), a coaxially-fed spiral antenna for biomedical telemetry is mentioned. The antenna includes a flat conductor on a dielectric material, above a ground plane, in an air-filled capsule.

After an IMD is implanted, it is generally surrounded by various bodily tissues or fluids. Such tissues or fluids (e.g., muscle tissue, fatty tissue, bone, blood, etc.) are somewhat conductive (e.g., lossy), inhomogeneous (e.g., having a varying loss and dielectric permittivity), and can have a relatively high dielectric permittivity as compared to free space. Because the medium surrounding the IMD in vivo can vary, and is different than a free space environment, the implantable antenna included as a portion of the IMD can be located at least partially within a dielectric compartment. Such a dielectric compartment can protect the implantable antenna from exposure to tissue or bodily fluids that may degrade antenna performance. Also, the dielectric compartment can improve operating consistency of the implantable antenna (e.g., a usable range, a directivity, a gain, or other performance) for both a free-space use environment before implant, and an in vivo environment after implant.

The present inventors have recognized, among other things, that the total volume of space occupied by an IMD can be an important consideration to both implanting physicians and patients. Thus, the size and shape of a dielectric compartment including the implantable antenna can be determined in part by spatial constraints (e.g., an allowable volume or surface area), and by biocompatibility considerations (e.g., a material or a shape can be selected to be compatible with, and unobtrusive to, the patient), rather than just electrical performance considerations. However, antenna length and volume are still generally governed by electrical performance needs as well. Generally, an antenna length, such as for a monopole antenna, can be about an odd-multiple of a quarter of a wavelength in a specified medium (e.g., ¼ of a wavelength, ¾ of a wavelength, etc.), corresponding to a desired resonant operating frequency within a desired operating frequency range.

As the desired operating frequency range decreases in frequency, the length and volume occupied by a relatively straight quarter-wavelength monopole (or half-wavelength dipole antenna) can become undesirably large, despite the higher relative dielectric permittivity of a tissue environment. For example, in some countries, wireless transfer of information can use a first specified range of frequencies around 900 megahertz (MHz), or some other range of frequencies, such as specified by a spectrum allocation authority. However, in other countries, or at the preference of a health care provider or caregiver, a second specified range of frequencies around 400 MHz may be used instead of, or in addition to, the first specified range of frequencies. For example, the operating frequency of radiofrequency (RF) telemetry in the Medical Implant Communications Service (MICS) band is about 402-405 MHz. The wavelength of an electromagnetic wave in the MICS band approximately can be calculated by following equation:

$\begin{matrix} {\lambda = \frac{c}{f\sqrt{ɛ_{req}}}} & {{Equation}\mspace{14mu} 1} \end{matrix}$ where in the above equation, c is the speed of the light, ∈_(req), is the equivalent relative dielectric constant of the antenna's surrounding material (e.g., header material and surrounding tissue) and f is the frequency.

The present inventors have recognized, among other things, that the total length of an antenna designed to work at around 900 MHz may need to more than double in order for such an antenna to be used at around 400 MHz. For example, Equation 1 suggests that the length of antenna in an implantable medical device operating in the MICS band should be about 10-12 centimeters (cm). Such a length may be unacceptable to end users because such a length may unacceptably increase the volume or area used by the implantable antenna.

From a clinician perspective, it may be desirable to fit the antenna within the header to reduce the size of the implantable medical device. However, the performance of the antenna can be degraded if it is too close to the housing, lead pins, and/or terminal blocks. In addition, as the medical devices become smaller, it becomes increasingly more difficult to design an antenna to fit within the device's header volume. The present inventors have recognized that it can be desirable to use electrically small antennas, e.g., where the actual length is less than a quarter of a wavelength in a specified medium. Antenna efficiency can generally be described by the following equation:

$\begin{matrix} {{{\left. {Effic} \right.\sim\frac{1}{BW}}\left( a_{k}^{3} \right)},} & {{Equation}\mspace{14mu} 2} \end{matrix}$ where BW is the antenna beamwidth and a_(k) is roughly equal to the volume enclosed by the antenna's longest dimension. Equation 2 shows that for an electrically small antenna, the antenna's efficiency is governed by the antenna volume. Although the electrically small antenna is easier to integrate within a header, its efficiency can be degraded from the ideal monopole: a quarter wavelength length when the antenna is a straight element normal to a ground plane.

Accordingly, the present inventors have also recognized that the implantable antenna can be made more compact than a straight monopole or straight dipole antenna, such as by using a more complex antenna shape, while still meeting design goals that constrain a total antenna volume or area. Moreover, the present inventors have recognized that such a compact antenna, such as including one or more of a spiral conductor (e.g., a conductive material arranged in a spiral pattern), or another shape (e.g., a serpentine conductor shape), can still have a physical path length approaching a quarter wavelength (or a half wavelength in the case of a dipole antenna). In an example, an implantable antenna including a spiral conductor can provide electrical performance comparable to a straight monopole (or dipole) conductor.

In an example, such a spiral conductor or other shape, such as a serpentine conductor shape, can be fabricated in a substantially planar pattern (e.g., etched, stamped, or cut out of a sheet of material in a relatively flattened pattern, such as providing a conductive pattern having a ribbon-shaped conductor cross section). Then, such a planar pattern can be formed or folded into a configuration to conform to, or extend along, one or more faces of the dielectric compartment. In an example, such a dielectric compartment can include a header attached to an IMD, the header including one or more connectors to electrically or mechanically mate with one or more implantable leads.

In an example, the disclosure is directed to an apparatus comprising an implantable medical device. The implantable medical device comprises a housing including an implantable telemetry circuit configured to wirelessly transfer information electromagnetically. The implantable medical device further comprises a dielectric compartment, mechanically coupled to the housing, the dielectric compartment including first and second substantially parallel face portions, and a third face portion extending between the first and second face portions. The implantable medical device further includes an antenna assembly configured to be mechanically attached to the dielectric compartment and electrically coupled to the implantable telemetry circuit, the antenna assembly including a spiral conductor comprising first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment, wherein the first, second, and third spiral conductor portions define an interior region, and wherein at least a portion of the third spiral conductor portion extends inwardly into the interior region.

In another example, the disclosure is directed to a method comprising providing an implantable medical device. The implantable medical device comprises a housing including an implantable telemetry circuit, the implantable telemetry circuit configured to wirelessly transfer information electromagnetically. The implantable medical device further includes a dielectric compartment, mechanically coupled to the housing, the dielectric compartment including first and second substantially parallel face portions, and a third face portion extending between the first and second face portions. The implantable medical device further including an antenna assembly configured to be mechanically attached to the dielectric compartment and electrically coupled to the implantable telemetry circuit, the antenna assembly including a spiral conductor including first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment, wherein the first, second, and third spiral conductor portions define an interior region, and wherein at least a portion of the third spiral conductor portion extends inwardly into the interior region. The method further includes wirelessly transferring information electromagnetically using the implantable antenna assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1 illustrates generally an example of an apparatus that can include an implantable medical device wirelessly coupled to an external module.

FIG. 2 illustrates generally an example of an apparatus that can include an implantable medical device, such as including an implantable telemetry circuit coupled to an implantable antenna including a spiral conductor.

FIGS. 3A-B illustrate generally examples of an apparatus that can include an implantable antenna located at least partially within a dielectric compartment.

FIGS. 4A-B illustrate generally examples of an apparatus, such as a portion of the apparatus of the examples of FIGS. 1-2, that can include a spiral conductor having a specified shape or configuration.

FIGS. 5A-C illustrate generally views of an example of at least a portion of an implantable antenna including a spiral conductor including a cross section having a lateral width that is greater than a sidewall height of the cross section, and having a specified separation between adjacent turns of the spiral conductor, and between the spiral conductor and another conductor.

FIGS. 6A-C illustrate generally views of an example of at least a portion of an implantable antenna, such as shown in the examples of FIG. 1-2, 3A, 4A-B or 5A-C, such as including a first conductive segment and a second conductive segment mechanically and electrically coupled using a specified transition portion.

FIGS. 7A-D illustrate generally a technique for fabricating a spiral conductor, such as shown in the examples of FIG. 1-2, 3A, 4A-B or 5A-C, such as including patterning or etching a planar conductor to provide a planar spiral pattern, and folding or forming the planar spiral pattern into a specified configuration.

FIGS. 8A-C illustrate generally an example of an apparatus that can include a modular implantable antenna assembly.

FIG. 9 illustrates generally an example of an apparatus that can include an implantable antenna comprising a loading portion.

FIGS. 10A-B illustrate generally an example of an apparatus that can include an implantable antenna including a spiral conductor.

FIGS. 11-18 illustrate generally examples of an apparatus that can include an implantable antenna including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range, the examples including various dielectric compartment and housing configurations.

FIGS. 19A-B, 20A-B, 21A-B illustrate generally examples of an apparatus that can include an implantable antenna including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range, the examples including various dielectric compartment and housing configurations.

FIG. 22 illustrates generally an example of technique that can include providing an implantable medical device including an implantable telemetry antenna, and wirelessly transferring information electromagnetically using the implantable telemetry antenna.

FIGS. 23A-B illustrate generally an example of an apparatus that can include a modular implantable antenna assembly.

FIGS. 24A-B illustrate generally an example of an apparatus that can include a modular implantable antenna assembly.

FIGS. 25A-B illustrate generally an example of an apparatus that can include a modular implantable antenna assembly.

FIGS. 26A-26D illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range.

FIGS. 27A-B illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range.

FIGS. 28A-B illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range.

FIGS. 29A-B illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range.

FIGS. 30A-B illustrate generally another example of a spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range.

DETAILED DESCRIPTION

FIG. 1 illustrates generally an example of an apparatus 100 that can include an implantable medical device (IMD) 102 implanted within a body (e.g., a patient 101), wirelessly coupled to an external module 115. In an example, the IMD 102 can include an implantable device housing 105 including a conductive portion (e.g., a hermetically-sealed titanium housing, or a housing including one or more other materials). For example, the housing 105 can contain at least a portion of an implantable telemetry circuit 106, such as a transmitter, a receiver, or a transceiver, configured to wirelessly transfer information electromagnetically using an implantable antenna 110 included at least partially within a dielectric compartment 107. In an example, the external module 115 can include an external antenna 117 coupled to an external telemetry circuit 116.

In an example, the external module 115 can include a physician programmer, a bedside monitor, or other relatively nearby assembly used to transfer programming instructions or configuration information to the IMD 102, or to receive diagnostic information, a disease status, information about one or more physiologic parameters, or the like, from the IMD 102. The external module 115 can be communicatively connected to one or more other external assemblies, such as a remote external assembly 175, located elsewhere (e.g., a server, a client terminal such as a web-connected personal computer, a cellular base-station, or another wirelessly-coupled or wired remote assembly). The implantable antenna 110 can include a spiral conductor, or one or more other conductor shapes or configurations, such as shown and discussed in the examples below.

FIG. 2 illustrates generally an example of an apparatus 200 that can include an IMD 202, including an implantable telemetry circuit 206 coupled to an implantable antenna 210 including a spiral conductor 209B. In the example of FIG. 2, the spiral conductor 209B can be fed by a conductive segment 209A. The conductive segment 209A can be substantially perpendicular to a surface or face of a housing 205, such as the housing 205 that comprises a conductive portion. For example, the conductive segment 209A can include a loading portion configured to adjust an input impedance of the implantable antenna 210, to provide an input impedance within a specified input impedance range at a specified range of frequencies. In an example, the conductive segment 209A can be used to reduce or eliminate a capacitive contribution to the input impedance of the implantable antenna 210, such as by reducing a capacitive interaction between the conductive segment 209A and the housing 205.

In an example, at least a portion of the implantable antenna 210 can be located at least partially on or within a dielectric compartment 207. For example, the dielectric compartment can include a biocompatible material such as an epoxy, a thermoplastic polyurethane (e.g., TECOTHANE™), or one or more other materials. In an example, the dielectric compartment can comprise a header including one or more connectors configured to mate with an implantable lead assembly, such as shown in the examples of FIG. 8-9, 10A-B, 11-18, 19A-B, 20A-B, or 21A-B. In an example, one or more of the spiral conductor 209B or the conductive segment 209A can include a ribbon shape or other cross section, such as shown in the examples of FIG. 8-9, 10A-B, 11-18, 19A-B, 20A-B, or 21A-B. In an example, the spiral conductor 209B can instead be replaced by one or more other conductive shapes, such as the serpentine conductor of FIG. 3B.

FIGS. 3A-B illustrate generally examples of an apparatus, such as a portion of the apparatus of the examples of FIGS. 1-2, that can include an implantable antenna located at least partially within a dielectric compartment 307. In the example of FIG. 3A, an antenna 310 including a spiral conductor can be located at least partially within the dielectric compartment 307 (e.g., a header, or another portion of an IMD, such as discussed in the examples above or below). In the example of FIG. 3A, the spiral conductor 310 can be oriented to extend along a first face 308A, a second face 308B, or a third face 304, of the dielectric compartment 307. For example, the first and second faces 308A-B can be substantially parallel (e.g., the sidewalls of the dielectric compartment 307). In an example, a third face 304 can extend between the first and second faces 308A-B, such as shown in FIG. 3A. In an example, the various faces of the dielectric compartment 307 need not be perfectly planar. In an example, the dielectric compartment 307 can be formed by one or more molding steps, such as using a thermosetting or a thermoplastic dielectric material.

In an example, unlike a helical or conical antenna, the spiral conductor 310 can include multiple “turns” in a plane perpendicular to a hypothetical axis. For example, for a portion of the spiral conductor 310 extending along the first face 308A, the turns of the spiral conductor can be “wound” concentrically in a plane substantially parallel to the first face 308A, along a hypothetical longitudinal axis 350. In an example, such as in FIG. 3A, each “turn” need not be circular. For example, for a portion of the spiral conductor 310 extending along the second face 308B, the turns can be again “wound” in a plane substantially parallel to the second face 308B, along the hypothetical longitudinal axis 350. In the example of FIG. 3A (and as similarly shown in the examples of FIGS. 7A-D), the planar spiral pattern can be folded to extend along more than one face of the dielectric compartment 307, such as to place the implantable antenna 310 at a specified depth from one or more of the first or second faces 308A-B, or the third face 304.

In the example of FIG. 3B, a serpentine antenna 312 can be similarly located on or within the dielectric compartment 307, such as including a first segment 313A extending along the first face, 308A, the second face 308B, and the third face 304. In the example of FIG. 3B, unlike the spiral conductor example of FIG. 3A, the instantaneous direction of a current flowing through the serpentine antenna 312, such as at or near resonance, can include a first direction (e.g., indicated by an arrow in FIG. 3B) associated with the first segment 313A. In such an example, the instantaneous current flowing through a second segment 313B, or a third segment 313C, can include a second, opposite, direction. In the example of FIG. 3B, the second and third segments 313B-C can extend along the lateral edges of the first segment 313A. However, if the first-third segments 313A-C are about the same depth from an exterior face of the dielectric compartment 307, the net radiated electromagnetic field is reduced as compared to the example of FIG. 3A. The decrease in the net radiated field can be due in part to a cancellation effect from the first and second current directions. For example, the electromagnetic field generated by the current flowing in the first direction is counteracted by the respective field contributions from the adjacent segments having respective currents flowing in the second, opposite, direction.

The present inventors have recognized that this cancellation effect can be reduced somewhat by staggering the depths of the various segments with respect to an exterior face of the dielectric compartment 307. For example, in FIG. 3B, the first-third segments 313A-C are relatively uniform in spacing from the first and second faces 308A-B. In an example, the third segment 313 could be relatively further recessed within the dielectric compartment 307, as compared to the first and second segments 313A-B. Similarly, the first segment 313A could be recessed further into the dielectric compartment than the second segment 313B, but not quite as far recessed as the third segment 313C. In an example, staggering the depths of the first, second and third segments 313A-C can also reduce unwanted coupling between adjacent segments (e.g., due to a fringing field effect). Such unwanted coupling can generally increase the capacitive portion of the input impedance of the antenna, and can at least partially “short out” the current flowing on the antenna, reducing the antenna's effective length or radiation efficiency, for example.

FIGS. 4A-B illustrate generally examples of an apparatus, such as a portion of the apparatus of the examples of FIGS. 1-2, that can include a spiral conductor 410A-B having a specified shape or configuration. In the example of FIG. 4A, a spiral conductor (e.g., similar to the spiral conductors included as a portion of the antenna 110, 210, or 310 shown in the examples of FIGS. 1-2, 3A) can include a specified distance between adjacent turns, “d₁.” The spiral conductor 410A can also include a conductor having a specified lateral width, “w₁.” In the example of FIG. 4A, the distance, “d₁,” can be relatively uniform (e.g., constant) along the path of the spiral conductor 410A. In FIG. 4A, the lateral width, “w₁,” can taper (or otherwise vary in a specified or controlled manner) along the path of the spiral conductor 410A.

Similarly, FIG. 4B illustrates an example where a lateral width, “w₂,” can taper (or otherwise vary in specified or controlled manner), along the path of the spiral conductor 410B, while a distance, “d₂,” between adjacent turns of the spiral conductor 410B can be relatively uniform. Such a tapering in either lateral width, or separation distance, or both, can be used at least in part to adjust or provide one or more desired electrical performance characteristics of an antenna including the spiral conductor 410A. For example, such adjustment can be used to provide a specified input impedance, a specified antenna gain, a specified directivity, or a specified current distribution along the antenna, or the like.

FIGS. 5A-C illustrate generally views of an example of at least a portion of an implantable antenna 510 including a spiral conductor. In the example of FIG. 5A, the antenna 510 can be monopole-like, such as using a conductive region 505 as a counterpoise (e.g., a reflector). In an example, an implantable antenna can include a dipole antenna (or another antenna type), such as using two (or more) similar spiral conductors each similar to the antenna 510 shown in FIGS. 5A-C. In such a dipole example, a counterpoise such as the conductive region 505 need not be included.

The antenna 510 can include a cross section having a lateral width, “w,” such as shown in FIG. 5B with respect to a first segment 510A in a first turn of the spiral conductor. In the examples of FIGS. 5A-C, the lateral width, “w,” can be greater than a sidewall height, “h,” of the cross section, again shown with respect to the first segment 510A in FIG. 5B. A specified separation, “d,” can be used between adjacent turns of the spiral conductor, such as shown in FIG. 5B, between the first segment 510A in the first turn, and a second segment 510B in a second turn of the spiral conductor.

The present inventors have recognized, among other things, that various undesired effects such as current cancelation or fringing-field effects can be reduced or eliminated using various techniques. Such techniques can allow the spacing, “d,” to be reduced as compared to antennas lacking such features as shown in FIGS. 5A-C. Such a reduction in spacing, “d,” can provide an antenna 510 that is more compact (e.g., volumetrically, or in surface area) than antennas lacking such features as shown in FIGS. 5A-C. For example, use of a spiral conductor geometry as shown in FIGS. 5A-C can reduce current cancelation versus using the serpentine geometry of FIG. 3B, because the instantaneous currents in adjacent segments (e.g., segments 510A-C) generally flow in the same direction when the antenna is operating in a first resonant mode.

Another technique can include staggering adjacent segments or turns of the antenna 510 in depth, such as locating a third segment 510C in the region 510D, such as to reduce an interaction between adjacent segments due to a fringing field 599 (e.g., an electric field indicative of capacitive coupling between adjacent segments). While such a modification to the location of segment 510C can result in an antenna 510 that is not perfectly planar, such an antenna is still substantially planar, since the change in the position of the segment 510C to the location of the region 510D can be very small, such as represented by “o,” in comparison to the total surface area of the plane of the antenna 510. For example, FIG. 5A can represent a view of a plane along a hypothetical axis 550 on which the antenna 510 is “wound.” The dimension, “o,” can represent an offset in depth between adjacent “turns” of the antenna, along the hypothetical axis 550. In an example, the total depth of the antenna 510 along such a hypothetical axis 550 can be at least an order of magnitude smaller than a diameter or a largest linear dimension. “l,” of the antenna 510.

Yet another technique can include using an antenna 510 including ribbon-shaped cross section, such as a rectangular cross section as shown in FIGS. 5A-C, or an otherwise non-circular cross section, instead of using a wire or round cross section. The present inventors have recognized, among other things, that the antenna 510 including spiral conductor using a ribbon cross section, as shown in FIGS. 5A-C, can be made more compact than a corresponding helical antenna or wire antenna. For example, the fringing field 599 interaction between adjacent segments can be reduced if the ribbon conductor is oriented so that the thinner sidewalls are adjacent to one another as compared to locating the “fat” lateral portions of width “w” facing one another.

The illustrative examples of FIGS. 9, 10A-B, 11-18, 19A-B, 20A-B, and 21A-B generally show the interaction between various physical parameters such as including the dimensions “w,” “h,” “d,” and “s.” In an illustrative example, if the antenna 510 is to be used for wireless transfer of information electromagnetically at a specified range of frequencies around 400 MHz, then the width, “w,” can be from a range of about 34 mils (0.034 inches) to about 50 mils (0.050 inches), or some other width. Generally, the sidewall height, “h,” can be kept small for the reasons discussed above, but the thickness should not be so small that surface roughness increases resistance undesirably. In an illustrative example, a ribbon thickness (e.g., sidewall height, “h”) can be larger than a “skin depth” of current at the desired operating frequency. At around 400 MHz, the skin depth is around 1 mil (0.001 inches). Thus, in such an illustrative example at 400 MHz, a surface roughness of about 0.1 mil (0.0001 inches) or less can be specified.

In an illustrative example, the distance between adjacent turns of the spiral conductor, “d,” can be from about 15 mils (0.015 inches) to about 20 mils (0.020 inches), or some other distance, such as for providing consistent performance at a specified range of frequencies around 400 MHz, in both free space (e.g., air) or in a variety of different tissue media. Though the antenna 510 can be made more compact using a closer spacing of adjacent turns, such a closer spacing can result in a higher quality factor, “Q,” corresponding to a reduced usable bandwidth as compared to an antenna having a wider spacing between adjacent turns.

In the example of FIG. 5C, the antenna 510 can be oriented so that the short sidewall of the spiral conductor is substantially parallel to the nearby conductive region 505. The conductive region 505 can be at “ground” potential for alternating current signals, thus a separation, “s,” between a segment 510E and the conductive region 505 can be maintained, such as to avoid unwanted loading of the antenna 510 by the conductive region. Similar to the discussion above with respect to adjacent segments, orienting the segment 510E so that the short sidewall is adjacent to the conductive region 505 can allow a smaller separation, “s,” than if the antenna had a round (e.g., wire) cross section, or if the antenna segment 510E were rotated 90 degrees so that the wider portion were closest to the conductive region 505. Thus, an antenna 510 can be “tucked” into a physically constrained area within a dielectric compartment, such as at the rear portion of a header for an IMD, while still maintaining a specified offset distance between the antenna 510 and adjacent conductive structures, such as a conductive housing of the IMD.

FIGS. 6A-C illustrate generally views of an example of at least a portion of an implantable antenna, such as shown in the examples of FIG. 1-2, 3A-B, 4A-B or 5A-C, such as including a first conductive segment and a second conductive segment mechanically and electrically coupled using a specified transition portion.

The examples of FIGS. 1-2, 3A, and 4A-B illustrate generally that an antenna for an IMD can include a spiral conductor. However, the spiral conductor need not include bends, radii, or transition portions for each turn that are the same for every turn, or for every junction between adjacent segments within a respective turn. In the example of FIG. 6A, a first segment 696A, such as ribbon-shaped conductor, can transition into a second segment 697A, such as using a 90-degree corner 698A. In the example of FIG. 6B, a first segment 696B can transition into a second segment 697B, such as via a “clipped” corner 698B. In the example of FIG. 6C, a first segment 696C can transition into a second segment 697C, such as using a radiused transition 698C. In an example, as operating frequency increases (e.g., an operating wavelength becomes shorter), power bundling or a concentration in current can occur if a sharp corner 698A or a clipped corner 698B is included, such as shown respectively in FIGS. 6A-B. For example, to avoid an unwanted peak in current magnitude, such as in a first or outer-most turn of an implantable antenna including a spiral conductor, the radiused transition of FIG. 6C can be used. Conversely, in an example, to provide a higher current density for one or more interior turns toward the center of the spiral conductor pattern, a sharper transition can be used, such as shown in the examples of FIG. 19A-B, 20A-B, or 21A-B. Such heightened current density on one or more interior turns can enhance radiation efficiency, while avoiding such sharp or clipped corners 698A-B on outer turns can help prevent an unwanted increase in a resistive contribution to an input impedance of the antenna.

FIGS. 7A-D illustrate generally a technique for fabricating a spiral conductor, such as shown in the examples of FIG. 1-2, 3A, 4A-B or 5A-C, such as including patterning or etching a planar conductor to provide a planar spiral pattern, and folding or forming the planar spiral pattern into a specified configuration. In FIG. 7A, a sheet of conductive material 701 can be provided (e.g., a sheet of metal stock, etc.). Such material 701 can include one or more of aluminum, steel, stainless steel, a biocompatible alloy (e.g., platinum-iridium or another material), or a shape-memory material (e.g., a nickel-titanium alloy or other material). In an example, one or more portions of an implantable antenna can be patterned, etched, cut, stamped, or otherwise formed from the sheet of conductive material 701, such as to provide a substantially planar spiral conductor 702 as shown in FIG. 7B. In an example, such a conductor 702 can have a ribbon-shaped cross section, such as including a lateral width of a segment determined by the shape of the pattern, and including a sidewall height of the segment determined by the thickness of the sheet of stock 701.

In an example, the material 701 can be a conductive material cladding a dielectric material. For example, the material 701 can include one or more of copper, aluminum, gold, platinum, or one or more metals or alloys, such as cladding a flexible or rigid dielectric substrate. In an example, the dielectric substrate can include one or more of a polyimide, polytetrafluoroethylene (PTFE), expanded PTFE (ePTFE), polyether-ether-ketone (PEEK), a thermoplastic polyurethane, an epoxy, a glass-epoxy laminate, or one or more other flexible or rigid materials. In such a cladded example, the material 701 can be etched or patterned to provide a desired conductor geometry, similar to the conductor 702, such as fabricated using one or more processes or techniques generally used for printed circuit board (PCB) or printed wiring board (PWB) manufacturing.

In an example, the conductor 702 can then be folded, bent, or otherwise formed into a desired two- or three-dimensional configuration, such as folded around a hypothetical axis 703, as shown in FIG. 7C, to provide an implantable antenna 710 having a specified configuration. In the example of FIG. 7D, the implantable antenna 710 can include a first substantially planar portion 705, and a second substantially planar portion 704. One or more of the first or second portions 704-705 can be overmolded, attached, inserted, or otherwise coupled to a dielectric material (e.g., a dielectric compartment included as a portion of an IMD), such that one or more of the first or second portions 704-705 extends along or is substantially parallel to a face of the dielectric material. In an example, the conductor 702 can be folded along more than one axis, such as shown in the example of FIG. 8, and elsewhere. In an example, one or more techniques similar to those shown in the examples of FIGS. 7A-D can be used, but instead including a serpentine antenna conductor pattern, such as shown in the example of FIG. 3B.

FIGS. 8A-C illustrate generally an example of an apparatus that can include a modular implantable antenna assembly. In an example, an IMD can include a first dielectric portion 807A, and a second dielectric portion 807B. The second dielectric portion 807B can include a header the IMD, such as configured for attachment to a conductive housing. For example, the header can provide one or more mechanical or electrical connections to one or more implantable lead assemblies, An implantable antenna including a spiral conductor 810 can be located in an otherwise unused portion of the header.

In an example, the first dielectric portion 807A can be a dielectric shell, such as including an interior-facing surface sized and shaped to accommodate the spiral conductor 810. For example, the first portion 807A can include one or more cavities, slots, stakes, ridges or other structures such as to provide or maintain a desired spacing or geometry for the spiral conductor 810, such as to avoid deforming the spiral conductor 810 in an unwanted manner during manufacturing.

In the example of FIG. 8A, the first dielectric portion 807A can be configured to have two substantially parallel interior faces (e.g., vertical sidewalls), and a portion extending between the two substantially parallel interior faces (e.g., the rear portion), to provide a “u”-shaped shell. In an example, the spiral conductor 810 can be inserted into or otherwise attached to the interior-facing surface of the u-shaped first dielectric portion 807A, such as using an injection (e.g., insert molding process),

In an examples of FIGS. 8B-C, the combination of the spiral conductor 810 and the first dielectric portion 807A can then be attached to a desired location on the second dielectric portion 807B (e.g., such as using a medical adhesive including silicone, or using an overmolding process, or one or more other techniques). For example, use of the modular assembly technique as shown in FIG. 8 can provide a desired separation between the spiral conductor 810 and a conductive housing of the IMD.

FIG. 9 illustrates generally an example of an apparatus 900 that can include an implantable antenna comprising a loading portion 910A, and a spiral conductor portion 910B, such as located within a dielectric material 907. In an example, the dielectric compartment 907 can be a header attached to an IMD housing, as discussed in the examples above, such as including a lead bore 970 configured to receive an implantable lead assembly. In the example of FIG. 9, the loading portion 910A can include a different conductor cross section than the spiral conductor portion 910B, such as to adjust an input impedance of the implantable antenna to achieve a specified input impedance range within a specified operating frequency range. For example, the spiral conductor portion 910B can provide an input impedance in both free space and in vivo that includes a relatively large capacitive component. The loading portion 910A can be used, at least in part, to reduce such a capacitive component of the input impedance. In an example, the loading portion 910A can include one or more other conductor shapes or configurations, such as a coil, a helix, a conductive segment oriented vertically with respect to the housing of the IMD, or one or more other conductor shapes, cross sections, or orientations. In an example, the spiral conductor portion 910B can instead be replaced with one or more other conductor geometries, such as a serpentine conductor shown in the example of FIG. 3B.

In the example of FIG. 9, one or more adjacent segments in the spiral conductor portion can be offset in depth from one another, such as discussed in the examples of FIGS. 5A-C. For example, such an offset in depth can help reduce an unwanted capacitive interaction between adjacent segments due at least in part to a fringing field effect.

FIGS. 10A-B illustrate generally an example of an apparatus 1000 that can include an implantable antenna 1010 that can include a spiral conductor. In the examples of FIGS. 10A-B, the spiral conductor can be located within a dielectric compartment 1007 (e.g., a header of an IMD), such as in a region not otherwise occupied by or near a lead bore 1070 or associated mechanical features (e.g., away from one or more contacts associated with a lead connector assembly, or away from a set-screw assembly, etc.). In an example, such as shown in FIG. 10B, the antenna 1010 can be shaped or formed so that a specified separation is maintained between the antenna 1010 conductor, and a nearby conductor such as a housing of the IMD, such as shown near the region 1016. Such a configuration can provide less electrical loading of the antenna 1010 by the housing 1005, as compared to an antenna including a portion as shown in the shaded regions 1017A-B.

FIGS. 11-18 generally show various illustrative examples of an apparatus that can include an implantable antenna 1110, 1210, 1310, 1410, 1510, 1610, 1710, or 1810 including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range, the examples including various dielectric compartment and housing configurations, such as included as a portion or part of an IMD.

In the examples of FIGS. 11-18, an IMD housing 1105, 1205, 1305, 1405, 1505, 1605, 1705, or 1805 of each example IMD 1100, 1200, 1300, 1400, 1500, 1600, 1700, and 1800, respectively, can include a conductive portion, such as a hermetically-sealed, laser-welded titanium enclosure, such as containing one or more circuit assemblies. Such circuit assemblies can include one or more electrostimulation or physiologic sensing circuits, such as coupled to one or more implantable lead assemblies via a connector assembly 1170, 1270, 1370, 1470, 1570, 1670, 1770, or 1870, located within or as a portion of a dielectric compartment 1107, 1207, 1307, 1407, 1507, 1607, 1707, or 1807. In the examples of FIGS. 11-18, various dielectric compartment configurations can be used, such as determined by how many implantable lead assemblies will be used (if any). Also, a number of electrodes or a number of lead wires included in a respective lead assembly can vary from one dielectric compartment 1107, 1207, 1307, 1407, 1507, 1607, 1707, or 1807 to another. For example, a multi-polar lead connector can provide respective connections within the dielectric compartment 1107, 1207, 1307, 1407, 1507, 1607, 1707, or 1807 to respective conductors connected to various electrical inputs or outputs of circuitry within the housing (e.g. via a hermetically-sealed filtered feedthrough assembly). The present inventors have also recognized that using an antenna with a spiral conductor configuration “tucked” into otherwise unused space in the dielectric compartment 1107, 1207, 1307, 1407, 1507, 1607, 1707, or 1807 may allow a common antenna design to be used across different dielectric compartment or housing configurations, such as reducing manufacturing complexity or increasing design flexibility.

In the examples of FIGS. 11-18, one or more physical parameters of the spiral conductor can be adjusted, such as to provide specified electrical operating characteristics within a specified operating frequency range. As in the examples of FIGS. 5A-C, a number of turns of the spiral conductor, the lateral width of the spiral conductor, the sidewall height of the spiral conductor, a separation between adjacent turns of the spiral conductor, a path length along the spiral conductor, a total surface area of the antenna 1110, 1210, 1310, 1410, 1510, 1610, 1710, or 1810, a diameter of a hypothetical sphere sized to enclose the antenna 1110, 1210, 1310, 1410, 1510, 1610, 1710, or 1810, or a separation between an end and an initial location along the antenna 1110, 1210, 1310, 1410, 1510, 1610, 1710, or 1810 can affect various electrical characteristics of the antenna 1110, 1210, 1310, 1410, 1510, 1610, 1710, or 1810. Such electrical characteristics can include a total radiated power (TRP), a radiation an efficiency, a directivity, or an input impedance, either in free space (e.g., air), or after implant in tissue. For example, TRP can be determined with respect to a reference power level, such as 1 milliwatt, and simulated or measured in decibel (e.g., logarithmic) units (e.g., dBm). Similarly, the directivity can be determined relative to an isotropic radiator, and simulated or measured in decibel units (e.g., dBi).

The illustrative examples of FIGS. 11-18 can be simulated using an electromagnetic modeling software package, such as Microwave Studio®, provided by Computer Simulation Technology, CST AG, Darmstadt, Germany. For example, TABLE 1, below, includes results of simulation performed on the illustrative examples of FIGS. 11-18 to estimate various antenna 1110, 1210, 1310, 1410, 1510, 1610, 1710, or 1810 electrical performance characteristics. Similarly, TABLE 2 illustrates generally various antenna conductor dimensions corresponding to the various illustrative examples provided in TABLE 1.

TABLE 1 Antenna Simulation Results for Various Illustrative Examples TRP - Impedance - TRP - Impedance - in Directivity - Air Air Directivity - in vivo vivo in vivo Example (Ohms) (dBm) Air (dBi) (Ohms) (dBm) (dBi) FIG. 11 7 - j120 −27 1.9 25 - j30 −23 2.12 FIG. 12 7 - j135 −33 1.85 22 - j51 −27 2.25 FIG. 13 9 - j150 −36 1.85 22 - j66 −29 2.27 FIG. 14 8.5 - j135   −28 1.87 26 - j41 −25 2.15 FIG. 15 9 - j147 −36 1.88 27 - j54 −28 2.4 FIG. 16 9 - j134 −35 1.89 27 - j42 −27 2.4 FIG. 17 8 - j135 −33 1.88 23 - j37 −26 2.3 FIG. 18 9 - j140 −34 1.88 34 - j25 −25 2.3

TABLE 2 Antenna Conductor Dimensions Spacing Total Ribbon between ribbon Width - turns - length Example “w” (mils) “d” (mils) (inches) FIG. 11 50 20 4.14 FIG. 12 50 20 3.25 FIG. 13 50 20 3.25 FIG. 14 45 15 4.8 FIG. 15 34 15 4 FIG. 16 45 15 3.8 FIG. 17 45 20 3.8 FIG. 18 45 20 4.5

FIGS. 19A-B, 20A-B, 21A-B illustrate generally examples of an apparatus 1900, 2000, or 2100, that can include an implantable antenna 1910B, 2010B, or 2110B including a spiral conductor 1910A, 2010A, or 2110A, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range, the examples including various dielectric compartment and housing configurations. In the illustrative examples of FIGS. 19A-B, 20A-B, and 21A-B, the spiral conductor 1910A, 2010A, or 2110A can be etched, stamped or otherwise formed (such as shown in the examples of FIGS. 7A-C and elsewhere) to provide a substantially planar conductor, such as including a ribbon-shaped conductor cross section. A portion 1919, 2019, or 2119 of the spiral conductor 1910A, 2010A, or 2110A can be sized and shaped to provide an electrical attachment or bonding point, such as to allow an electrical coupling to be made between the antenna 1910B, 2010B, or 2110B and circuitry within a housing 1905, 2005, or 2105 of an IMD.

In an example, the antenna 1910B, 2010B, or 2110B can be folded or otherwise formed into a desired configuration, such as located within a dielectric compartment 1907, 2007, or 2107 away from one or more electrical connectors for one or more implantable lead assemblies, such as a first lead bore 1970, 2070, or 2170. In an example, such as shown in FIGS. 19B, 20B, and 21B, the antenna 1910B, 2010B, or 2110B can substantially conform to the contour of one or more exterior faces of the dielectric compartment 1907, 2007, or 2107, such as to maintain a specified depth within the compartment, or to maintain a specified separation between the housing 1905, 2005, or 2105 and the antenna 1910B, 2010B, or 2110B.

In the example of FIG. 20B, the antenna 2010B is spaced slightly further away from the housing 2005 as compared to the example of FIG. 19B. Similarly, in the example of FIG. 21B, the antenna 2110B is spaced slightly further away from the lead connectors, such as the first lead bore 2170, as compared to the examples of FIGS. 19B and 20B. TABLE 3 illustrates generally various antenna simulation results and physical dimensions corresponding to the antennas 1910B, 2010B, and 2110B of FIGS. 19B, 20B, and 21B. In the illustrative examples of FIGS. 20B-21B, the spacing between adjacent turns, “d,” can taper or vary along the path of the antenna 2010B, or 2110B, thus a range of values are included in TABLE 3.

TABLE 3 Antenna Simulation Results and Dimensions for Various Illustrative Examples Spacing Ribbon between Total TRP - TRP - in Width - turns - ribbon Overall Air vivo “w” “d” length height Example (dBm) (dBm) (mils) (mils) (inches) (inches) FIG. 19B −34 −25 45 25 4.514108 0.478 FIG. 20B −34 −26 45 2.5-15 4.460559 0.48 FIG. 21B −35 −28 45 21.5-25 3.876241 0.483

FIG. 22 illustrates generally an example of technique 2200 that can include, at 2202, providing an implantable medical device including an implantable telemetry antenna, such as shown in one or more of the examples of the previous figures. At 2204, the technique 2200 can include wirelessly transferring information electromagnetically using the implantable telemetry antenna, such as shown in the examples of FIGS. 1-2, for an implantable antenna included as a portion of an IMD.

FIGS. 23A-B illustrate generally an example of an apparatus that can include a modular implantable antenna assembly. In the example of FIG. 23A, a dielectric core 2380 can be formed, such as injection molded using an epoxy or urethane compound. A portion of the dielectric core 2380 can be insert-molded or otherwise formed to include one or more set-screw blocks or other structures. For example, a spiral conductor 2310 can form a portion of an antenna, such as discussed in the examples above. A portion of the dielectric core 2380 can be insert-molded or otherwise bonded to mechanically retain the spiral conductor 2310. Then, a dielectric compartment 2307 can be overmolded or otherwise formed to contain the dielectric core 2380, and the spiral conductor 2310, such as to provide an implantable assembly. For example, the implantable assembly shown in FIG. 23B can include a header, such as to provide an electrical or mechanical connection to one or more implantable leads, such as via a lead cavity or “bore” 2370. Such a header can then be mechanically attached to an implantable medical device housing, as discussed in the examples above. In the example of FIGS. 23A-B, the dielectric core can include two substantially parallel face portions, such as in the side-wall regions of the core 2380. The spiral conductor can be conformed or otherwise shaped to extend along a portion of the two substantially parallel faces as shown in FIGS. 23A-B, and a central portion of the spiral conductor 2310 can extend along a surface of the core 2380, such as comprising a third face extending between the two side-wall regions of the core 2380. Such a configuration provides a more omni-directional antenna configuration while still efficiently using the available volume within the dielectric compartment 2307. In an example, the dielectric core 2380 can include a channel or one or more stakes, such as to retain or immobilize the spiral conductor 2310 prior, during, or after a molding operation or one or more other fabrication steps. In a stake example, the spiral conductor 2310 can include a hole or one or more other structures, and a stake can penetrate through or can otherwise retain the spiral conductor 2310, such as after the stake is pressed or deformed, using either acoustic energy, heat, or one or more other techniques.

FIGS. 24A-B illustrate generally an example of an apparatus that can include a modular implantable antenna assembly. In the example of FIG. 24A, similar to the example of FIG. 23A, a dielectric core 2480 can be formed, such as injection molded or insert-molded to include one or more set-screw blocks or other structures. Then, a dielectric compartment 2407B can be overmolded or otherwise formed around the dielectric core. Unlike the example of FIGS. 23A-B, a module implantable antenna assembly can be configured similarly to the examples of FIGS. 8A-C. For example, the dielectric compartment 2407B can include a cavity, a channel, or a general area where a dielectric shell 2407A can be attached. In an example, the dielectric shell 2407A can be “U”-shaped, such as including an exterior-facing portion, and an interior-facing portion. In the example of FIG. 24A, the spiral conductor 2410 (such as a portion of an implantable antenna assembly) can be located on the interior-facing portion of the dielectric shell 2407A. In an example, the dielectric shell 2407A can be insert-molded around the spiral conductor 2410, such as to retain the antenna 2410. Then, in the example of FIG. 24B, similarly to the examples of FIGS. 8A-C, the combination of the dielectric shell 2407A and the spiral conductor 2410 can be attached to the dielectric compartment 2407B, such as to immobilize the spiral conductor 2410. As in the examples above, the dielectric compartment can be a header configured to provide an electrical or mechanical connection to one or more implantable leads, such as via a lead bore 2470. As with all the examples discussed above and below, the dielectric compartment 2407B need not be homogeneous or all-dielectric throughout its entire volume. For example, in FIG. 24B, one or more set-screw blocks, connecting wires, or other structures can be included within the dielectric compartment. In an example, a portion of the dielectric compartment 2407B can be hollow or can include a cavity or a channel. Such a cavity or a channel can initially be open, but can be later filled or overmolded with dielectric material such as an adhesive, a back-fill material, or one or more other materials, such as after making one or more internal electrical or mechanical connections, or such as after attachment of the dielectric shell 2407A to the dielectric compartment 2407B.

FIGS. 25A-B illustrate generally an example of an apparatus that can include a modular implantable antenna assembly. In FIG. 25A, a dielectric core 2580 can be formed, such as molded or otherwise fabricated to include a cavity or channel. The cavity or channel can be sized and shaped to complement a spiral conductor 2510, such as to retain or align the spiral conductor 2510. In an example, the core 2580 can be insert-molded around a portion of the spiral conductor 2510. In an example, the core can include a stake or other structure. Such a stake or other structure can be used to attach the spiral conductor 2510 to the core. In the example of FIG. 25B, a dielectric compartment 2507 can contain the dielectric core 2580 and spiral conductor 2510. For example, the dielectric compartment 2507 can be formed by overmolding the dielectric core 2580, or by placing the antenna assembly comprising the core 2580 and spiral conductor 2510 into a cavity within the dielectric compartment 2507, and then backfilling any remaining space in the cavity with medical adhesive or one or more other compounds. The dielectric compartment 2507 can include one or more other structures, such as a set screw block or other mechanical or electrical connections, such as to provide an interface for an implantable lead via a lead connector 2570.

In the examples of FIGS. 23A-B, 24A-B, and 25A-B, similar to the examples of FIGS. 8A-C, a modular antenna assembly can be fabricated, such as tailored to a specific location of use (e.g., for use at a specified range of frequencies, or for use with a particular model of implantable medical device). Such a modular assembly can allow an antenna configuration to be specified or selected for use with a specified implantable medical device assembly (e.g., pairing a particular antenna assembly to a desired implantable medical device configuration, such as during manufacturing). Also, such a modular design can allow revision to the antenna assembly, such as to the spiral conductor, without requiring the rest of the dielectric compartment design to change, reducing the cost of development.

FIGS. 26A-26D illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range. FIGS. 26A-26C depict a perspective view, top view, and front view, respectively, of a spiral conductor 2610, and FIG. 26D depicts the implantable antenna assembly 2612 including the spiral conductor 2610 positioned within a dielectric compartment 2614 of an implantable medical device.

As shown best in the top-view of FIG. 26B, the spiral conductor 2610 can include a first portion 2616, a second portion 2618, and a third portion 2620, which can be configured to extend along or adjacent to first, second, and third face portions, respectively, on an interior surface of the dielectric compartment 2614 (FIG. 26D). The first and second portions 2616, 2618 of the spiral conductor 2610 can be conformed or otherwise shaped to extend along or adjacent to a portion of two substantially parallel faces of the dielectric compartment 2614, namely faces 2622, 2624. Also, the third, or central, portion 2620 of the spiral conductor 2610 can extend along or adjacent to a third face 2626 of the dielectric compartment 2614 that extends between the two parallel faces 2622, 2624.

The first, second, and, third portions 2616-2620 of the spiral conductor 2610 can define an interior region of the spiral conductor (shown at 2628 in FIG. 26B). In some examples, the spiral conductor 2610 can be cut out of a sheet of material in a relatively flattened pattern, such as providing a conductive pattern having a ribbon-shaped conductor cross section.

In some examples and in accordance with this disclosure, the spiral conductor 2610 can include one or more bends, e.g., bends 2630A-2630E (referred to collectively as “bends 2630”). The present inventors have recognized that, in one example implementation, by including one or more bends 2630 in the spiral conductor 2610, the volume of the antenna assembly can be reduced while maintaining the length of the antenna assembly.

Referring to FIG. 26B, which depicts a top view of the conductor 2610, the bend 2630A (representative of one or more of the bends 2630B-2630E of FIGS. 26A and 26C) of the spiral conductor 2610 can extend inwardly into the interior region 2628 of the spiral conductor 2610 defined by the portions 2616-2620. By adding one or more bends 2630, the length of either or both of the portions 2616 and 2618, for example, can be reduced, which can reduce the volume of the antenna assembly. Alternatively, by adding one or more bends 2630, the length of the antenna assembly can be increased without increasing the volume of the antenna assembly. In addition, the inclusion of one or more bends 2630 can cause discontinuities within the antenna. These discontinuities can improve the performance of the antenna, e.g., increase the gain of the antenna assembly.

As seen in the example configurations of FIGS. 26A-D, the bends 2630 can be located substantially halfway between the first and second substantially parallel face portions 2622, 2624 of the dielectric compartment 2614. In other example configurations, however, the bends 2630 can be offset such that they are closer to one face portion than the other (not depicted).

In some examples, the bends 2630 can be defined by a bend radius of a surface of the spiral conductor 2610. In some examples, the bend radius can have a range of about 0.005 inches (0.0127 centimeters) to about 0.085 inches (0.2159 centimeters). If the bends 2630 get too close to the header terminal, the antenna energy can be shunted back, thereby reducing the radiation of the antenna assembly.

As described above with respect to FIGS. 5A-C, the spiral conductor 2610 can include a cross section having a lateral width that is greater than a sidewall height of the cross section. In addition, a sidewall of one of the first, second, and third spiral conductor portions 2616-2620 can be oriented so that the sidewall provides a sidewall face that is substantially parallel to one of the first, second, and third face portions of the dielectric compartment.

In one example configuration, to provide a specified input impedance range within a specified range of operating frequencies, a separation between adjacent turns of the spiral conductor 2610 (as shown and described with respect to FIGS. 5A-5C) can be decreased. Decreasing the separation between adjacent turns of the spiral conductor 2610 can be performed in lieu of using a spiral conductor 2610 where the cross section has a lateral width that is less than the sidewall height, as described herein. In another example configuration, a total surface area of the spiral conductor 2610 can be increased. Increasing the surface area of the spiral conductor 2610 is another option to provide a specified input impedance range within a specified range of operating frequencies, rather than using a cross section lacking the lateral width greater than the sidewall height.

Referring to FIG. 26C, each of the five turns of the spiral conductor 2610 can include a single bend 2630. In some example configurations, each of the turns can include more than one bend 2630. In one example, some of the turns may not include a bend while other turns include one or more bends.

FIG. 26D depicts an apparatus 2632 that includes the implantable antenna assembly 2612, which can include the spiral conductor 2610. The spiral conductor 2610 can be configured to be mechanically attached to the dielectric compartment 2614. The apparatus 2632 can include an IMD housing 2636, such as described above with respect to FIGS. 11-18, for example. As seen in FIG. 26D, in some examples, the spiral conductor 2610 can comprise a spiral pattern including concentric turns, where the spiral pattern is folded so that a portion of the spiral pattern 2638 is located adjacent the third face portion 2626 of the dielectric compartment 2614. Additional aspects of the apparatus 2632 of FIG. 26D are similar to those described herein.

FIGS. 27A-B illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range. As seen in FIG. 27A, the spiral conductor 2710 includes six turns 2712A-2712F, in contrast to the five turns of the antenna 1710, for example, shown and described above with respect to FIG. 17.

By using an additional turn, as in FIG. 27A, the length of the antenna can be maintained while reducing the volume of the antenna. As mentioned above, reducing the volume of the antenna assembly may be desirable not only to reduce the size of the device, but also to increase a separation distance between the components in the header and the antenna assembly. If the antenna assembly is too close to the components in the header, e.g., components of the lead bore, energy can be coupled back to components in the header instead of being radiated outward from the antenna assembly, which can decrease the gain of the antenna assembly.

In some examples, the spiral conductor 2710 can be cut out of a sheet of material in a relatively flattened pattern, such as providing a conductive pattern having a ribbon-shaped conductor cross section. In one specific example, the width 2714 of the spiral conductor 2710 can be about 0.045 inches (0.1143 centimeters), the thickness can be about 0.015 inches (0.0381 centimeters), and the spacing between turns, shown at 2716, can be about 0.035 inches (0.0889 centimeters).

FIG. 27B depicts an apparatus 2718 that includes an implantable antenna assembly 2720, which can include the spiral conductor 2710. Like the spiral conductor 2610 of FIGS. 26A-D, the spiral conductor 2710 can include a first portion, a second portion, and a third portion, which can be configured to extend along first, second, and third face portions, on an interior surface of a dielectric compartment of the apparatus 2718. Additional aspects of the apparatus 2718 of FIG. 27B are similar to those described herein.

FIGS. 28A-B illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range. In contrast to the spiral conductors described above with respect to FIGS. 26A-D and FIGS. 27A-B, the spiral conductor 2810 is not conformed or otherwise shaped to extend along multiple faces of a dielectric compartment. Rather, as seen in FIG. 28B, the spiral conductor 2810 of the antenna 2812 can extend along a single face 2814 of the dielectric compartment 2816.

In some examples, the spiral conductor 2810 can be cut out of a sheet of material in a relatively flattened pattern, such as providing a conductive pattern having a ribbon-shaped conductor cross section. In one specific example, the width 2818 (FIG. 28A) of the spiral conductor 2810 can be about 0.045 inches (0.1143 centimeters), the thickness can be about 0.015 inches (0.0381 centimeters), and the spacing between turns, shown at 2820, can be about 0.035 inches (0.0889). Using a ribbon-shaped conductor cross section on the end of the antenna 2812 can provide a large surface area to store charge, like capacitor plates.

FIG. 28B depicts an apparatus 2822 that includes the implantable antenna assembly 2812, which can include the spiral conductor 2810 of FIG. 28A and a long conductor 2824 that extends around various components of the header 2826 and then connects to the feedthrough assembly at 2828. In some examples, the long conductor 2824 can be a wire having a substantially round cross-section.

The present inventors have recognized that the current density is highest at the beginning, or proximal end, of the antenna assembly 2812 at the point of connection to the power source, shown at 2828, and that the long conductor 2824 can be passed around the components of the header 2826 while keeping the spiral conductor 2810 away from the header components, thereby preventing the spiral conductor 2810 from substantially coupling to the header components. The antenna assembly 2812 may not couple to the header components because most of the capacitive coupling appears at the distal end 2830 (FIG. 28A) of the antenna assembly 2812, where the concentration of charge is highest. As such, the antenna assembly 2812 can be passed around the components of the header 2826 without reducing the effective length of the antenna 2812. In this manner, the spiral conductor 2810 and the long conductor 2824 can allow the antenna assembly 2812 to be physically closer to the header components, thereby reducing the size of the apparatus.

The present inventors have also recognized that the impedance of the antenna assembly 2812 having the spiral conductor 2810 of FIG. 28A can be comparable in both air and tissue. As such, one compensation network may optimize the antenna's radiation in both air and tissue. This is in contrast to other designs in which the impedance of the antenna assembly may be substantially different in air and in tissue. In such antennas, the compensation network may optimize the radiation in either air or tissue, not both.

Additional aspects of the apparatus 2822 of FIG. 28B are similar to those described herein.

The illustrative examples of FIGS. 27A and 28A can be simulated using an electromagnetic modeling software package, such as Microwave Studio®, provided by Computer Simulation Technology, CST AG, Darmstadt, Germany. For example, TABLE 4, below, includes results of simulation performed on the illustrative examples of FIGS. 27A and 28A to estimate the electrical performance characteristics of antennas 2720 and 2812.

TABLE 4 Antenna Simulation Results for Various Illustrative Examples Impedance - Air Impedance - in Total Efficiency Example (Ohms) vivo (Ohms) (dB) FIG. 27A 4.4 − j138.4 14.3 − j24.8 −36.15 FIG. 28A 3.7 − j31   9.2 + j5.5 −23.52

FIGS. 29A-B illustrate generally another example of an implantable antenna assembly including a spiral conductor, the spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range. Like the spiral conductor 2810 described herein with respect to FIGS. 28A-B, the spiral conductor 2910 of the antenna assembly 2912 can extend along a single face 2914 of the dielectric compartment 2916 rather than along multiple faces of the dielectric compartment, as seen in FIG. 29B. The effective lengths of the spiral conductor 2910 and the spiral conductor 2710 of FIG. 27A are approximately the same as long as their physical lengths are identical and the distance between the outermost edges of the turns are identical.

In some examples, the spiral conductor 2910 can be formed from a wire having a substantially round cross-section. In one specific example, the wire can have a diameter of about 0.015 inch (0.0381 centimeters) to about 0.030 inch (0.0762 centimeters) and the spacing between turns, shown at 2918 of FIG. 29A, can be about 0.045 inches (0.1143 centimeters). In some examples, the spacing 2918 between the turns can be constant, such as shown in FIG. 29A. In other examples, the spacing 2918 between the turns can be variable (not depicted). For example, the spacing 2918 could be 0.045 inches (0.1143 centimeters) at the center of the spiral conductor 2910, but the spacing 2918 could be reduced toward the outer turns, which could reduce the size of the antenna.

By using a wire with a substantially round cross-section, the spacing 2918 between the turns of the spiral conductor 2910 can be increased. Because the turn capacitive coupling is proportional to the surface area of the conductor divided by the distance between the turns, increasing the spacing 2918 between the turns can reduce the capacitive coupling, which can increase the effective length of the antenna. If the distance 2918 is kept constant, within the same volume, more wire turn can be implemented, resulting in a longer antenna length.

FIG. 29B depicts an apparatus 2920 that includes the implantable antenna assembly 2912, which can include the spiral conductor 2910 of FIG. 29A and a short connector portion 2922 that connects to the feedthrough assembly at 2924, like the short connectors of FIG. 26D and FIG. 27B. Additional aspects of the apparatus 2920 of FIG. 29B are similar to those described herein.

FIGS. 30A-B illustrate generally another example of a spiral conductor sized and shaped to provide specified electrical operating characteristics within a specified operating frequency range. In some examples, the spiral conductor 2910 of FIGS. 29A-B can have a conical shape, such as shown in FIGS. 30A-B. FIGS. 30A-B depict a side view and front view, respectively, of a conical helical spiral conductor 3010. The conical design of the spiral conductor 3010 can increase the spacing between the turns, thereby increasing the effective length of the spiral conductor 3010.

Additional Notes

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, the code can be tangibly stored on one or more volatile or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 

The invention claimed is:
 1. An apparatus, comprising: an implantable medical device comprising: a housing including an implantable telemetry circuit configured to wirelessly transfer information electromagnetically; a dielectric compartment mechanically coupled to the housing, wherein the dielectric compartment includes first and second substantially parallel face portions, and a third face portion extending between the first and second face portions; an antenna assembly configured to be mechanically attached to the dielectric compartment and electrically coupled to the implantable telemetry circuit, the antenna assembly including a spiral conductor comprising a planar spiral pattern folded into first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment, wherein the first, second, and third spiral conductor portions define an interior region, wherein at least a portion of the third spiral conductor portion extends inwardly into the interior region, and wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region includes a surface defining a curvature that has a bend radius.
 2. The apparatus of claim 1, wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region is located substantially halfway between the first and second substantially parallel face portions of the dielectric compartment.
 3. The apparatus of claim 1, wherein the spiral pattern comprises concentric turns.
 4. The apparatus of claim 3, wherein the spiral conductor includes at least five turns.
 5. The apparatus of claim 1, further comprising an implantable lead, the implantable lead including an electrode configured for location at a tissue site, and coupled to electronic circuitry within the housing to provide one or more of electrostimulation of tissue or sensing of activity, at the site of the electrode, wherein the dielectric compartment comprises a header configured to provide an electrical and mechanical connection to the implantable lead.
 6. The apparatus of claim 1, wherein the spiral conductor includes a cross section having a lateral width that is greater than a sidewall height of the cross section.
 7. The apparatus of claim 6, wherein a sidewall of one of the first, second, or third spiral conductor portions is oriented so that the sidewall provides a sidewall face that is substantially parallel to one of the first, second, or third face portions of the dielectric compartment.
 8. The apparatus of claim 6, wherein a separation between adjacent turns of the spiral conductor is decreased to provide a specified input impedance range within a specified range of operating frequencies.
 9. The apparatus of claim 6, wherein a total surface area of the spiral conductor is increased to provide a specified input impedance range within a specified range of operating frequencies.
 10. A method comprising: providing an implantable medical device comprising: a housing including an implantable telemetry circuit configured to wirelessly transfer information electromagnetically; a dielectric compartment mechanically coupled to the housing, where the dielectric compartment includes first and second substantially parallel face portions, and a third face portion extending between the first and second face portions; an antenna assembly configured to be mechanically attached to the dielectric compartment and electrically coupled to the implantable telemetry circuit, the antenna assembly including a spiral conductor comprising a planar spiral pattern folded into first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment, wherein the first, second, and third spiral conductor portions define an interior region, wherein at least a portion of the third spiral conductor portion extends inwardly into the interior region, and wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region includes a surface defining a curvature that has a bend radius; and wirelessly transferring information electromagnetically using the implantable antenna assembly.
 11. The method of claim 10, wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region is located substantially halfway between the first and second substantially parallel face portions of the dielectric compartment.
 12. The method of claim 10, wherein the spiral pattern comprises concentric turns.
 13. The apparatus of claim 12, wherein the spiral conductor includes at least five turns.
 14. The method of claim 10, further comprising an implantable lead including an electrode configured for location at a tissue site, and coupled to electronic circuitry within the housing to provide one or more of electrostimulation of tissue, or sensing of activity, at the site of the electrode, and wherein the dielectric compartment comprises a header configured to provide an electrical and mechanical connection to the implantable lead.
 15. The method of claim 10, wherein the spiral conductor includes a cross section having a lateral width that is greater than a sidewall height of the cross section.
 16. The method of claim 15, comprising: orienting a sidewall of one of the first, second, or third spiral conductor portions so that the sidewall provides a sidewall face that is substantially parallel to one of the first, second, or third face portions of the dielectric compartment.
 17. The method of claim 10, further comprising: providing the spiral conductor with the spiral pattern that includes concentric turns; and folding the spiral pattern so that a portion of the spiral pattern is located adjacent the third face portion of the dielectric compartment. 